题目：
The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)
P A H N
A P L S I I G
Y I R
"PAHNAPLSIIGYIR"
Write the code that will take a string and make this conversion given a number of rows:
string convert(string text, int nRows);
convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".
解法：
class Solution(object): def convert(self, s, numRows): """ :type s: str :type numRows: int :rtype: str """ if numRows == 1 or numRows >= len(s): return s L = [‘‘] * numRows index, step = 0, 1 for x in s: L[index] += x if index == 0: step = 1 elif index == numRows -1: step = -1 index += step return ‘‘.join(L) c = Solution() print c.convert("PAYPALISHIRING", 3)
1.通过索引和步长来解题，当走到头时，改变step的方向
2. [""] * n 可以创建空字符列表。